Setting Up PCA9685

Step-by-step guide on connecting the PCA9685 servo driver to the Raspberry Pi and testing it with Python to control servos.

By Kevin McAleer,    3 Minutes

Preparing for Servo Control

In this lesson, we’ll take a closer look at how to properly set up the PCA9685 servo driver with your Raspberry Pi and write a simple Python script to test servo control. This is a crucial step in bringing our robot arm to life.

Equipment Needed

• Raspberry Pi (with Python and necessary libraries installed)
• PCA9685 servo driver board
• Servos (at least one for testing)
• External power supply for servos (5-6V)
• Jumper wires

Connection Overview

Ensure your Raspberry Pi is turned off before making any connections to prevent damage. Connect the PCA9685 to the Raspberry Pi as follows:

1. VCC to Raspberry Pi 5V
2. GND to Raspberry Pi GND
3. SCL to Raspberry Pi SCL (GPIO 3)
4. SDA to Raspberry Pi SDA (GPIO 2)

Connect your external power supply to the PCA9685, and then connect a servo to one of the PCA9685’s channels, ensuring the orientation of the wires is correct.

Testing the Connection

With the hardware set up, let’s write a simple Python script to test controlling a servo.

Step 1: Import Libraries

from Adafruit_PCA9685 import PCA9685
from time import sleep

Step 2: Initialize PCA9685

pwm = PCA9685()
pwm.set_pwm_freq(60)  # Set frequency to 60Hz

Step 3: Control a Servo

We’ll make the servo connected to channel 0 move back and forth.

channel = 0
min_pulse = 150  # Min pulse length out of 4096
max_pulse = 600  # Max pulse length out of 4096

while True:
    pwm.set_pwm(channel, 0, min_pulse)
    sleep(1)
    pwm.set_pwm(channel, 0, max_pulse)
    sleep(1)

This script sets the servo to its minimum position, waits a second, moves it to its maximum position, and waits again in a continuous loop.

Conclusion

You have now successfully set up the PCA9685 servo driver with your Raspberry Pi and tested it by controlling a servo. This foundational knowledge will be invaluable as we proceed to design and program the movements of our robot arm.

Lesson Assignment

Experiment with different values for min_pulse and max_pulse to see how they affect the servo’s movement. Try connecting and controlling multiple servos on different channels of the PCA9685.